Converted more of std.datetime's examples to ddoc-ed unit tests.

The ones at the end which are removed from the docs are removed because
they're private, so there's no point in having an example in their
documentation.
Merge pull request #2205 from jmdavis/datetime

Converted more of std.datetime's examples to ddoc-ed unit tests.
add NullSink output range
Merge pull request #2030 from WalterBright/add-BitBucket2

add BitBucket output range
fix Issue 7822 - lseek cast(int)offset should be lseek cast(off_t)offset
Merge pull request #2209 from SerialVelocity/master

Fix Issue 7822 - lseek cast(int)offset should be lseek cast(off_t)offset